Ion milling device and ion milling method

Abstract

To provide an ion gun of a penning discharge type capable of narrowing a beam with a low ion beam current at a low acceleration voltage, an ion milling device including the same, and an ion milling method. An ion milling device that controls half width of a beam profile of an ion beam with which a sample is irradiated from an ion gun to be in a range of 200 μm to 350 μm. The device includes: the ion gun that ionizes a gas supplied from the outside, and emits an ion beam; a gas-flow-rate varying unit that varies a flow rate of the gas supplied to the ion gun; and a current measurement unit that measures a current value of the ion beam emitted from the ion gun. The gas-flow-rate varying unit sets a gas flow rate to be higher than a gas flow rate at which the ion beam current has a maximum value based on the current value measured by the current measurement unit and the flow rate of the gas determined by the gas-flow-rate varying unit.

The invention claimed is: 
     
       1. An ion milling device that controls a half width of a beam profile of an ion beam with which a sample is irradiated from an ion gun to be in a range of 200 μm to 350 μm, the device comprising:
 the ion gun that ionizes a gas supplied from the outside, and emits an ion beam; 
 a gas-flow-rate varying unit that varies a flow rate of the gas supplied to the ion gun; and 
 a current measurement unit that measures a current value of the ion beam emitted from the ion gun, 
 wherein the gas-flow-rate varying unit is set to control a gas flow rate to be higher than a gas flow rate at which the current value measured by the current measurement unit has a maximum value, and such that a width of the beam profile of the ion beam at a point halfway between a topmost depth of the beam and a bottommost depth of the beam is reduced in relation to a width of the beam at the topmost depth by increasing the gas flow rate to which the gas-flow-rate varying unit is set, and 
 wherein the beam profile is based on a relationship between a beam diameter or width with respect to a spot depth of the beam. 
 
     
     
       2. The ion milling device according to  claim 1 ,
 wherein a voltage ranging from 2 kV to 4 kV is applied to an acceleration electrode of the ion gun. 
 
     
     
       3. The ion milling device according to  claim 1 ,
 wherein an outlet diameter of an acceleration electrode is 2 mm. 
 
     
     
       4. The ion milling device according to  claim 1 , further comprising:
 a heat transfer unit that transfers heat from the sample and a sample support to a cooling source. 
 
     
     
       5. The ion milling device according to  claim 1 ,
 wherein the gas is selected from the group consisting of an inert gas and a reactant gas. 
 
     
     
       6. The ion milling device according to  claim 1 ,
 wherein the gas is argon. 
 
     
     
       7. The ion milling device according to  claim 6 ,
 wherein the argon gas is supplied to the ion gun at a flow rate of 0.3 to 0.5 cubic centimeters per minute. 
 
     
     
       8. The ion milling device according to  claim 6 ,
 wherein the argon gas is supplied to the ion gun at a flow rate of 0.3 cubic centimeters per minute or more. 
 
     
     
       9. The ion milling device according to  claim 1 ,
 wherein the ion gun is a penning discharge type. 
 
     
     
       10. An ion milling method of controlling a half width of a beam profile of an ion beam to be in a range of 200 μm to 350 μm, and processing a sample, the method comprising:
 an emission step of ionizing a gas supplied from the outside, and emitting the ion beam; 
 an application step of applying a voltage ranging from 2 kV to 4 kV to an acceleration electrode of an ion gun; 
 a flow-rate varying step of varying a flow rate of the gas supplied to the ion gun; 
 a measurement step of measuring a current value of the ion beam emitted from the ion gun; 
 a setting step of setting a gas flow rate to be higher than a gas flow rate at which the ion beam current has a maximum value based on the current value measured in the measurement step; and 
 an irradiation step of irradiating the sample with the ion beam set in the setting step, 
 wherein a width of the beam profile of the ion beam at a point halfway between a topmost depth of the ion beam and a bottommost depth of the ion beam is controlled to be smaller than a half width of the beam profile of the ion beam in relation to a width of the beam at the topmost depth and at which the ion beam current has the maximum value set in the setting step, and 
 wherein the beam profile is based on a relationship between a beam diameter or width with respect to a spot depth of the beam.